based messaging protocol, similar in concept to
HTTP sessions, but with session state maintained by
one of the AMA servers, and with responses to time-consuming operations returned asynchronously.

Each active user has one or more active sessions,which has loaded all the data related to a schedulethat user is working on. This speeds the client-serverinteraction, especially when editing schedulingrequests and activities, when there can be numerousincremental schedule changes.

Next we discuss some of the challenges related to
modeling (DSN services, multiple simultaneous
spacecrafts, nonlocal time line constraints) and
schedule generation and repair algorithms. We also
discuss the design of service aliases inasmuch as they
underpin all of the DSE functionality.